PROGRESSION OF GLACIERS. 
275 
teme Glaciaire ” show to exist, only when it 
is below 82° Fahrenheit. If it be contended 
that ice at 82° does break, and that therefore 
the whole mass of the glacier may break at 
that temperature, setting aside the contradic- 
tion to the facts of regelation which such an 
assumption involves, I would refer to Dr. 
Tyndall’s experiments concerning the vacuous 
spots iu the ice. 
Those who have read his startling investiga- 
tions will remember that by sending a beam 
of sunlight through ice he brought to view 
the primitive crystalline forms to which it 
owes its solidity, and that he insisted that these 
star-shaped figures are always in the plane of 
crystallization. Without knowing what might 
he their origin, I had myself noticed these fig- 
ures, and represented them in a diagram, part of 
which is reproduced in the accompanying wood- 
